LONDON, June 24 (Reuters) - U.S. cyber attacks against Iranian targets have not been successful, Iran's telecoms minister said on Monday, after reports that the Pentagon had launched a long-planned cyber attack to disable his country's rocket launch systems.

Tension is running high between longtime foes Iran and the United States after U.S. President Donald Trump on Friday said he called off a military strike to retaliate for Iran's downing of a U.S. drone.

However, Yahoo News reported on Thursday that the United States had launched cyber attacks, even as Trump backed away from a conventional attack.

The Washington Post said on Saturday that the cyber strikes, which were previously planned, had disabled Iranian rocket launch systems. U.S. officials have declined to comment.

"They try hard, but have not carried out a successful attack," Mohammad Javad Azari Jahromi, Iran's minister for information and communications technology, said on Twitter.

"Media asked if the claimed cyber attacks against Iran are true," he said. "Last year we neutralised 33 million attacks with the (national) firewall."

Azari Jahromi called attacks on Iranian computer networks "cyber-terrorism", referring to Stuxnet, a computer virus widely believed to have been developed by the United States and Israel, which was discovered in 2010 after it was used to attack a uranium enrichment facility in the Iranian city of Natanz.

The United States has also accused Iran of stepping up cyber attacks.

Iran's foreign ministry spokesman, Abbas Mousavi, said Iran's cyber defence system was strong, and that Iran could legally pursue such aggression in international courts.

He was quoted by ISNA news agency as saying that Tehran welcomed "defusion of tensions" in the region.

"We do not want rise of tensions and its consequences."

Last year, Trump withdrew the United States from a 2015 accord between Iran and world powers that curbed Tehran's nuclear programme in exchange for easing sanctions. Relations in the region have worsened significantly since then.

Trump said on Sunday he was not seeking war with Iran and would be prepared to seek a deal to bolster its flagging economy, an apparent move to defuse tensions.

Trump has suggested that he backed off a military strike against Iran because he was not sure the country's top leadership had intended to shoot down the drone. However, an Iranian commander said Tehran was prepared to do it again.

"Everyone saw the downing of the unmanned drone," navy commander Rear Admiral Hossein Khanzadi was quoted on Sunday as saying by the Tasnim news agency. "I can assure you that this firm response can be repeated, and the enemy knows it." (Reporting by Bozorgmehr Sharafedin Editing by Clarence Fernandez, Robert Birsel)